Power steering system and a method of operating same

ABSTRACT

A method for controlling a power steering system utilizes a vehicle having a motor, a controller coupled to the motor, and a steering assembly. The method includes detecting a steering rate using the controller and determining a vehicle speed. A base level steering damping is computed using the steering rate and the vehicle speed. At least one approximate vehicle acceleration is determined. A steering torque of the steering assembly is sensed through a torque sensor configured to sense the steering torque of the steering assembly. Moreover, a user torque is determined using the torque sensor. A damping boost is computed using the user torque and the at least one approximate vehicle acceleration. A final steering damping gain is determined using the base level steering damping and the damping boost. The final steering damping gain is applied to the steering assembly to minimize unwanted feedback to the steering assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

The subject patent application claims priority to and all the benefitsof International Application No. PCT/IB2017/051995, which was filed onApr. 6, 2017 with the World Intellectual Property Organization, thedisclosure of which is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a power steering system having acontrol logic and a method of operating the same.

BACKGROUND

Power steering systems are known in the prior art and often use adetected vehicle speed to determine a level of damping and apply thedamping to the steering assembly in order to provide stability to thesteering assembly. Typically, a mechanical damper is assembled on thesteering assembly to provide more stability of the steering assemblyregardless of vehicle speed.

Other power steering systems may compute and apply to the steeringassembly a level of damping using vehicle accelerations such asaccelerations in any direction including the x-direction, they-direction, and the z-direction. Again, a mechanical damper assembledon the steering assembly has a constant damping effect regarding thevehicle accelerations.

The current power steering systems, however, may still experienceinstability if used in recreational vehicles such as all-terrainvehicles, motorcycles, snowmobiles, etc. Specifically, when a driver isoperating the vehicle over rough terrain the driver may rotate thehandle bar or unexpectedly let go of the throttle on the handlebar.Similarly, the driver may forcefully engage the brake during operationover unexpectedly rough terrain. During these events, instability mayoccur to the handlebar or other steering elements which is felt by thedriver. As such, there remains a need for a control method whichprovides stability to the handlebar or other steering elements duringabrupt or unexpected changing of acceleration.

SUMMARY

A method for controlling a power steering system utilizes a vehiclehaving a motor, a controller coupled to the motor, and a steeringassembly. The method includes detecting a steering rate using thecontroller and determining a vehicle speed. A base level steeringdamping is computed using the steering rate and the vehicle speed. Atleast one approximate vehicle acceleration is determined. A steeringtorque of the steering assembly is sensed though a torque sensorconfigured to sense the steering torque of the steering assembly.Moreover, a user torque is determined using the torque sensor. A dampingboost is computed using the user torque and the at least one approximatevehicle acceleration. A final steering damping gain is determined usingthe base level steering damping and the damping boost. The finalsteering damping gain is applied to the steering assembly to minimizeunwanted feedback to the steering assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of an exemplary vehicle which mayincorporate a power steering system of the present invention.

FIG. 1B is a perspective view of another exemplary vehicle which mayincorporate the power steering system of the present invention.

FIG. 2 is a perspective view of a steering assembly of a vehicle whichmay incorporate the power steering system of the present invention.

FIG. 3 is a diagram illustrating an exemplary method for operating adamping control within the power steering system.

FIG. 4 is a block diagram illustrating an exemplary method for operatingthe damping control within the power steering system.

DETAILED DESCRIPTION

Referring to the Figures, an exemplary vehicle 10 is shown in FIGS. 1Aand 1B. The vehicle 10 may be a snowmobile, an all-terrain vehicle (ATV)such as a four wheeler, a three wheeler, and the like, a motorcycle orany other similar vehicle. However, it is also contemplated that thevehicle 10 may be any type of vehicle as known by one of ordinary skillin the art including a standard car, a full size or standard size truck,a semi-truck, and the like without departing from the spirit of theinvention.

FIG. 2 shows an exemplary steering assembly 12 of the vehicle 10. Thesteering assembly 12 includes a steering column 14 coupled to a steeringrack 16 which is coupled to ground engaging members 18. It is alsocontemplated that the steering assembly 12 may comprise any mechanicallink between the steering column 14 and the ground engaging members 18as known by one of ordinary skill in the art including but not limitedto linkages. The ground engaging members 18 may include a sled or tireas known by one of ordinary skill in the art. Generally, the groundengaging members 18 are coupled to steering rods 20. Movement of a useroperated steering element 22, such as a steering wheel as illustrated inFIG. 2, or a handlebar as illustrated in FIG. 1A on the vehicle 10causes movement of the steering rods 20 which turns the ground engagingmembers 18. It is additionally contemplated that the steering assembly12 may be a different user operated steering assembly which operates asknown by one of ordinary skill in the art.

The steering assembly 12 additionally includes a power steering system24. In the embodiment illustrated in the Figures, the power steeringsystem 24 is an electric power steering system. However, it iscontemplated that the power steering system 24 may be any power steeringsystem as known by one of ordinary skill in the art. The power steeringsystem 24 may be programmable such that the power steering system 24 canaccount for various vehicle conditions. In one exemplary embodiment, thepower steering system 24 includes a controller 26 which may receive anddeliver various inputs and outputs to and from various portions of thevehicle 10. Additionally, the controller 26 may execute variouscalculations and computations based on one or more inputs.

As additionally illustrated in FIG. 3, the power steering system 24 isconfigured to read or determine a vehicle speed 28. In one exemplaryembodiment, vehicle speed 28 may be determined using an RPM of thevehicle motor. It is also contemplated that the vehicle speed 28 may beread or determined by any other method as known by one of ordinary skillin the art including but not limited to a sensor or sensing system, acalculation based on one or more sensors, a value based on a dynamicdata table, or the like. Moreover, the vehicle speed 28 is used as aninput parameter of a dynamic data table in order to compute a portion ofa base level of steering damping 30. Specifically, the vehicle speed 28is used as an input parameter to compute G₁ 32 of the base level ofsteering damping 30. G₁ 32 is a calculated damping ratio based on thevehicle speed 28, as known by one of ordinary skill in the art. The baselevel of steering damping 30 is calculated using G₁ 32 and a steeringrate 34 which is further described below. In FIG. 3, the boxes having atleast one input and at least one output indicate that a calculation isbeing done using the at least one input to get a value for the at leastone output. It is contemplated that the calculation may be done by thecontroller 26 or another portion of the vehicle including but notlimited to a sensing system, the steering assembly, etc.

Continuing with FIG. 3, the vehicle speed 28 is a user defined variablewhich corresponds to G₁ 32, as illustrated in the graph of step 104. Itis also contemplated that the vehicle speed 28 may be used to calculateG₁ 32 by another method as known by one of ordinary skill in the art. Asadditionally illustrated in FIG. 3, a higher vehicle speed 28corresponds to a higher base level of steering damping 30. The powersteering system 24, more specifically the controller 26, may includevarious calibrated dynamic data tables in order to calculate andre-calculate the base level of steering damping 30 as known by one ofordinary skill in the art.

The power steering system 24 also is configured to determine, or receivefrom an external sensing system, a steering rate 34. It is contemplatedthat the steering rate 34 may be determined using a motor RPM of anelectric motor disposed within the steering assembly. However, it isalso contemplated that the steering rate 34 may be determined by anothermethod as known by one of ordinary skill in the art such as using asteering position sensor. The steering rate 34 has a direction which maycorrespond with a positive sign or a negative sign as illustrated inFIG. 3. In one embodiment, the steering rate 34 has a positive sign whenthe steering element 22 is moved or turned to the left and has anegative sign when the steering element 22 is moved or turned to theright. However, it is also contemplated that the positive and negativesign of the steering rate 34 may be opposite or in response to anotheroperation. Moreover, it is contemplated that the steering rate 34 isused as a proportional gain which is applied to G₁ 32 to compute thebase level of steering damping 30. It is contemplated that the baselevel of steering damping 30 is increased with an increased steeringrate 34 as illustrated in the graph of an exemplary dynamic data tableillustrated in FIG. 3. However, it is also contemplated that thesteering rate 34 and base level of steering damping 30 may be related inanother way. Moreover, it is contemplated that the contents of thedynamic data table may be based on consumer data gathered at a laterdate or may change over time.

Once the base level of steering damping 30 is determined, the base levelof steering damping 30 may then be applied to the steering assembly 12,as known by one of ordinary skill in the art. However, it is alsocontemplated that the base level of steering damping 30 is insteadmodified by the power steering system 24 by a damping boost 40 beforebeing applied to the steering assembly 12. The damping boost 40generally comprises a first damping boost, G₂ 42, which is calculatedusing a user torque 44 and the steering rate 34, and a second dampingboost, G₃ 46, which is calculated using approximate vehicleaccelerations 48. The damping boost 40 may be a positive or negativedamping boost 40 such that the damping boost 40 increases or decreasesthe base level of steering damping 30. The damping boost 40 may then beapplied to the base level of steering damping 30 to determine a finalsteering damping gain 50. The final steering damping gain 50 is thenapplied to the steering assembly 12 to help minimize unwanted feedbackto the steering assembly 12. Feedback may be electronic feedback whichresults in instability in the steering assembly 12, as known by one ofordinary skill in the art. It is contemplated that the final steeringdamping gain 50 may a positive or negative damping gain.

As illustrated in FIG. 3, the sign of the steering rate 34 isadditionally used in conjunction with the user torque 44 to define aninput 51 of the lookup table 108, which defines G₂ 42. Morespecifically, in one exemplary embodiment, the sign of the steering rate34 is multiplied by the user torque 44 to define input 51. It iscontemplated that G₂ 42 may be a positive or negative boost such thatthe damping boost 40 increases or decreases the base level of steeringdamping 30 as known by one of ordinary skill in the art. Morespecifically, it is contemplated that G₂ 42 may be a reducing ratio suchthat the value of G₂ 42 is less than 1. Therefore, the effect of thedamping boost 40 may reduce the base level of steering damping 30 whenthe steering column 14 moves with the applied user torque 44.

The user torque 44 may be sensed by a torque sensor 45 which may bebuilt within the electric power steering system. However, it iscontemplated that the user torque 44 may be sensed or determined byanother method as known by one of ordinary skill in the art. It is alsocontemplated that the torque sensor may be disposed in another locationwithin the vehicle 10 as desired by one of ordinary skill in the art.The torque sensor may be coupled to the steering shaft 15, may be incommunication with the controller 26, and may be configured to sensedeformation of the steering shaft 15. It is also contemplated that thetorque sensor may be configured to sense another measurable to determinethe user torque 44 such as measuring applied steering torque of thesteering shaft through the torque sensor, as known by one of ordinaryskill in the art.

The second portion of the damping boost 40, G₃ 46, is determined usingthe approximate vehicle accelerations 48. The approximate vehicleaccelerations 48 may be linear and/or angular accelerations and mayinclude, but are not limited to, throttle level, brake level, vehiclespeed, vehicle engine RPM, steering position, and acceleration. It isalso contemplated that the approximate vehicle accelerations 48 mayinclude other vehicle acceleration measurements as known by one ofordinary skill in the art. It is also contemplated that the approximatevehicle accelerations may include one or more, including two or more ofthe throttle level, the brake level, acceleration in any direction,vehicle speed, vehicle engine RPM, and steering position. The throttlelevel may be sensed or calculated using information from a throttlesensor, using information regarding the power output from the vehicle,by measuring vehicle responsiveness or otherwise determined by thevehicle 10 by a method as known by one of ordinary skill in the art. Inone exemplary embodiment, the torque sensor is disposed on a useroperated throttle device of the steering assembly and the throttle levelmay be determined using a level of the throttle device. The brake levelmay be sensed using a velocity sensors, an acceleration sensor, a forcesensor, a brake position sensor, a combination of any of the above, orusing other information determined by the vehicle 10. It is alsocontemplated that the brake level may be sensed or determined usinganother method as known by one of ordinary skill in the art. Moreover,the acceleration may include acceleration in any direction including thex-direction, the y-direction, or the z-direction. Additionally,acceleration in any direction may be sensed or determined using avelocity sensor, a gyrometer, an acceleration sensor, a force sensor, oranother method as known by one of ordinary skill in the art. In someapplications, acceleration may also include forces on a driver of thevehicle 10 and on the steering assembly 12. The forces on the steeringassembly 12 may result in undesired rotation of the steering assembly12. It is contemplated that the approximate vehicle accelerations may bedetermined by the controller or another controller or similar devicedisposed elsewhere within the vehicle. The damping boost 40 iscalculated and applied to the base level of steering damping 30 todetermine the final steering damping gain 50 which is applied to thesteering assembly 12 in order to mute or help control the undesiredrotation of the steering assembly 12.

As additionally illustrated in FIG. 3, G₃ 46 is calculated based on theapproximate vehicle accelerations 48. The approximate vehicleaccelerations 48 may be calculated based on available accelerationsignals, mathematic function, a dynamic data table as exemplaryillustrated in FIG. 3, or another dynamic data table as known by one ofordinary skill in the art. If there are no approximate vehicleaccelerations 48 for a specific application, then G₃ 46 is defined as aconstant equal to 1 such that no additional boost is necessary and thedamping boost 40 is calculated using only G₂ 42. It is contemplated thatG₃ 46 may be calculated by the graph of the dynamic data table asillustrated in FIG. 3, or may be calculated by another dynamic datatable or graph as known by one of ordinary skill in the art based on theapproximate vehicle accelerations 48, separately or together.

As described above and as illustrated in FIG. 3, the base level ofsteering damping 30 is multiplied by G₂ 42 and G₃ 46 which togethercomprise the damping boost 40 to determine the final steering dampinggain 50. The final steering damping gain 50 is applied to the steeringassembly 12 of the vehicle 10 in order to help control unwanted feedbackto the steering assembly 12. It is contemplated that the final steeringdamping gain 50 may be applied directly to the steering column 14 of thesteering assembly 12, or may be applied to another portion of thesteering assembly 12 as desired by one of ordinary skill in the art. Inone exemplary embodiment, the power steering system 24 is an electricpower steering system such that the final steering damping gain 50provides an electrical gain to an electric motor to minimize unwantedfeedback to the steering assembly 12. In another exemplary embodiment,the final steering damping gain minimized unwanted feedback to thesteering element 22.

In operation, and as illustrated in FIG. 4, the power steering system 24reads or determines the steering rate 34 of the vehicle 10 in step 102.At the same time, the power steering system 24 reads or determines thevehicle speed 28 in step 104. It is also contemplated that the steeringrate 34 and the vehicle speed 28 may be read or determined notsimultaneously, but one after another in any order as desired by one ofordinary skill in the art. The read or determined steering rate 34 alongwith the read or determined vehicle speed 28 are moved to the controller26 where the base level of steering damping 30 is calculated in step106. Simultaneously, the power steering system 24 reads or determinesthe user torque 44 in step 108. However, it is also contemplated thatthe user torque 44 may be read or determined prior to or after the baselevel of steering damping 30 is calculated. The user torque 44 and thesteering rate 34 are used to determine G₂ 42. Next, the power steeringsystem 24 reads or determines the approximate vehicle accelerations 48in step 110. Again, it is contemplated that the approximate vehicleaccelerations 48 may be read or determined before, after, or at the sametime as the user torque 44. The approximate vehicle accelerations 48 arethen used to calculate G₃ 46. Once the user torque 44 and approximatevehicle accelerations 48 are read or determined, G₂ 42 and G₃ 46 areused to determine the damping boost 40 in step 112. The damping boost 40and the base level of steering damping 30 current are then used tocompute the final steering damping gain 50 in step 114. Once the finalsteering damping gain 50 is calculated, the final steering damping gain50 is applied to the steering system in step 116. Specifically, thefinal steering damping gain 50 may be applied to the steering column 14.It is also contemplated that the final steering damping gain 50 may beapplied to another portion of the steering system such as the steeringrack, handlebar, or another portion as known by one of ordinary skill inthe art. The described method may then be constantly repeated while thevehicle 10 is powered on such that perpetual damping is applied to thesteering column 14 to provide a smooth ride of the vehicle 10 at alltimes. Moreover, it is contemplated that the above method may beperformed in any order, as desired by one of ordinary skill in the art.

The above described method avoids instability caused by rapiddeceleration of the vehicle 10. In one example, the vehicle 10 is asnowmobile or ATV which includes a handlebar accelerator and/or brake.When various forces such as perturbations from a road or trail act uponthe vehicle 10, the present method uses user torque 44 and approximatevehicle accelerations 48 to compute the damping boost 40 which willcombat this instability and provide a smooth ride to the driver duringthese times. Moreover, the above method will allow the user to easilycounter-steer the vehicle 10 during operation, including but not limitedto during rapid deceleration events. The vehicle 10 of the presentinvention may also include various limiters, filter, saturations, and avibration control which is also help stabilize the vehicle 10 duringvarious accelerations.

The invention has been described in an illustrative manner, and it is tobe understood that the terminology which has been used is intended to bein the nature of words of description rather than of limitation. Manymodifications and variations of the present invention are possible inlight of the above teachings, and the invention may be practicedotherwise than as specifically described.

What is claimed is:
 1. A method of controlling a power steering systemutilizing a vehicle having a motor, a controller coupled to the motor, atorque sensor, and a steering assembly, said method comprising the stepsof: determining a steering rate applied to the steering assembly usingthe controller; determining a vehicle speed; computing a base levelsteering damping using the steering rate and the vehicle speed;determining at least one approximate vehicle acceleration, wherein theapproximate vehicle acceleration is selected from the group of: throttlelevel, brake level, and acceleration; sensing a steering torque of thesteering assembly though the torque sensor; determining a user torquecalculated from the steering torque applied to the torque sensor;computing a damping boost using the user torque and the at least oneapproximate vehicle acceleration; computing a final steering dampinggain using the base level steering damping and the damping boost; andapplying the final steering damping gain to the steering assembly tominimize unwanted feedback to the steering assembly.
 2. The method asset forth in claim 1, wherein the step of applying the final steeringdamping gain is further defined as applying the final steering dampinggain to a steering column of the steering assembly of the vehicle. 3.The method as set forth in claim 1, wherein the steering assembly has asteering shaft with the torque sensor coupled to the steering shaft andin communication with the controller, and wherein the step of sensingthe steering torque is further defined as sensing the steering torque ofthe steering shaft using the torque sensor.
 4. The method as set forthin claim 1, further including a user operated throttle device having athrottle sensor, and wherein the step of determining the throttle levelof the approximate vehicle acceleration is further defined asdetermining a level of the user operated throttle device using thethrottle sensor.
 5. The method as set forth in claim 1, wherein the stepof determining the acceleration of the approximate vehicle accelerationis further defined as determining at least one of acceleration in an xdirection, acceleration in a y direction, acceleration in a z direction,and angular accelerations.
 6. The method as set forth in claim 1,wherein the steering assembly includes an electric motor and wherein thestep of determining the steering rate is further defined as detecting amotor RPM of the electric motor.
 7. The method as set forth in claim 1,wherein the step of computing the damping boost is further defined asusing the user torque, the at least one approximate vehicleacceleration, and a direction of the steering rate.
 8. The method as setforth in claim 7, wherein the step of computing the damping boost isfurther defined as modifying the user torque using the direction of thesteering rate to determine a modified user torque.
 9. The method as setforth in claim 8, wherein the damping boost comprises a first portionand a second portion, and wherein the step of computing the dampingboost is further defined as transforming the modified user torque to thefirst portion of the damping boost.
 10. The method as set forth in claim9, wherein the step of computing the damping boost is further defined astransforming the at least one approximate vehicle acceleration to thesecond portion of the damping boost.
 11. The method as set forth inclaim 1, wherein the step of determining the approximate vehicleacceleration is further defined as using two or more of the throttlerate, the braking rate, and acceleration to determine the approximatevehicle acceleration.
 12. The method as set forth in claim 1, whereinthe step of computing a base level steering damping is further definedas transforming the vehicle speed to a calculated damping ratio based onthe vehicle speed.
 13. The method as set forth in claim 1, wherein thepower steering system is an electric power steering system and whereinthe step of applying the final steering damping gain to the steeringassembly is further defined as providing an electrical gain to anelectric motor to minimize unwanted feedback to the steering assembly.14. The method as set forth in claim 1, wherein the steering assemblyincludes a steering element operated by a user and wherein the step ofapplying the final steering damping gain to the steering assembly isfurther defined as minimizing unwanted feedback to the steering element.15. A power steering system for a vehicle having a motor, said systemcomprising: a steering assembly for steering the vehicle; a torquesensor to sense a steering torque of said steering assembly; acontroller coupled to said steering assembly to determine a steeringrate applied to said steering assembly and to determine a vehicle speed,with said controller using the steering rate and the vehicle speed tocompute a base level steering damping, and said controller determining auser torque calculated from the steering torque applied to said torquesensor; wherein a damping boost is computed using the user torque and atleast one approximate vehicle acceleration with the at least oneapproximate vehicle acceleration selected from the group consisting of:throttle level, brake level, acceleration, and combinations thereof,wherein a final steering damping gain is computed using the base levelsteering damping and the damping boost, and wherein the final steeringdamping gain is applied to said steering assembly to minimize unwantedfeedback to said steering assembly.
 16. The system as set forth in claim15, wherein said steering assembly comprises a steering shaft and saidtorque sensor is coupled to said steering shaft for sensing the steeringtorque of said steering shaft.
 17. The system as set forth in claim 15,further comprising a user operated throttle device having a throttlesensor for determining the throttle level of the approximate vehicleacceleration.
 18. The system as set forth in claim 15, furthercomprising an electric motor, and wherein the steering rate isdetermined by detecting a motor RPM of said electric motor.
 19. Thesystem as set forth in claim 15, wherein the power steering system is anelectric power steering system, and wherein an electric gain is providedto an electric motor when the final steering damping gain is applied tosaid steering assembly.
 20. The system as set forth in claim 15, whereinsaid steering assembly includes a steering element operated by a userand the final steering damping gain is applied to said steering assemblyto minimize unwanted feedback to said steering element.